Ellipsometry is a well known means by which to monitor material systems, (samples). In brief, a polarized beam of electromagnetic radiation of one or more wavelengths is caused to impinge upon a material system, (sample), along one or more angles of incidence and then interact with a material system, (sample). Beams of electromagnetic radiation can be considered as comprised of two orthogonal components, tie. “P” and “S”), where “P” identifies a plane which contains both an incident beam of electromagnetic radiation, and a normal to an investigated surface of a material system, (sample), being investigated, and where “S” identifies a plane perpendicular to the “P” plane and parallel to said surface of said material system, (sample). A change in polarization state in a polarized beam of electromagnetic radiation caused by said interaction with a material system, (sample), is representative of properties of said material system, (sample). (Note polarization state basically refers to a magnitude of a ratio of orthogonal component magnitudes in a polarized beam of electromagnetic radiation, and a phase angle therebetween.) Generally two well known angles, (PSI and DELTA), which characterize a material system, (sample), at a given angle-of-incidence, are determined by analysis of data which represents change in polarization state. Additional sample identifying information is often also obtained by application of ellipsometry, including layer thicknesses, (including thicknesses for multilayers), optical thicknesses, sample temperature, refractive indicies and extinction coefficients, index grading, sample composition, surface roughness, alloy and/or void fraction, parameter dispersal and spectral dependencies on wavelength, vertical and lateral inhomogenieties etc.
Continuing, ellipsometer systems generally include a source of a beam of electromagnetic radiation, a polarizer means, which serves to impose a linear state of polarization on a beam of electromagnetic radiation, a stage for supporting a material system, (sample), and an analyzer means which serves to select a polarization state in a beam of electromagnetic radiation after it has interacted with a material system, (sample), and pass it to a detector system for analysis therein. As well, one or more compensator(s) can be present and serve to affect a phase angle change between orthogonal components of a polarized beam of electromagnetic radiation. It is noted that to obtain acceptable ellipsometer and/or polarimeter performance over a wide spectral range, compensator-based ellipsometer and/or polarimeter designs require a compensator element that provides retardance within a certain acceptable range over the entire spectral range. Traditionally, birefringent waveplates of quartz or MgF2 have been used as compensator elements in rotating element designs. A single waveplate exhibits a (1/wavelength) dependence in retardance vs. wavelength, while a dual/multiple waveplate design, (as disclosed in U.S. Pat. No. 6,353,477), can minimize the effect of the (1/wavelength) dependence.
Continuing, spectroscopic ellipsometer systems utilize a source which simultaneously provides a plurality of wavelengths, which Source can be termed a “broadband” source of electromagnetic radiation. It is disclosed that sources of ultraviolet wavelength electromagnetic radiation which produce wavelengths between below 245 nm and 1100 nm at usable intensities, without generation of significant levels of ozone are known. A problem inherent in operation, however, is that to increase intensity output therefrom or extend the useable wavelength range lower limit to say 220 nm or even 160 nm and below, results in increased heat production and accompanying production of levels of ozone to which personnel can not be safely exposed. The temperature of the source can be controlled by flowing a gas therearound to dissipate increased heat, but this also serves to unacceptably distribute produced ozone into surrounding atmosphere when it is produced. It has also been discovered that flowing a cooling gas around a source of ultraviolet wavelength electromagnetic radiation serves to modulate intensity output. While not limiting, a source of ultraviolet wavelength electromagnetic radiation which can stabily provide increased intensity output and/or shorter wavelengths, while not distributing accompanying produced ozone to surrounding atmosphere, or causing operator accessible outer extents thereof to exceed about 50 C, might supplement the present invention.
A number of types of ellipsometer systems exist, such as those which include rotating elements and those which include modulation elements. Those including rotating elements include rotating polarizer (RP), rotating analyzer (RA) and rotating compensator (RC). The presently disclosed invention comprises a rotating compensator ellipsometer system. It is noted that rotating compensator ellipsometer systems do not demonstrate “dead-spots” where obtaining data is difficult. They can read PSI and DELTA of a material system over a full range of degrees with the only limitation being that if PSI becomes essentially zero (0.0), one can't then determine DELTA as there is not sufficient PSI polar vector length to form the angle between the PSI vector and an “X” axis. In comparison, rotating analyzer and rotating polarizer ellipsometers have “dead spsots” at DELTA's near 0.0 or 180 Degrees and modulation element ellipsometers also have “dead spots” at PSI near 45 Degrees. The utility of rotating compensator ellipsometer systems should then be apparent. Another benefit provided by fixed polarizer (P) and analyzer (A) positions is that polarization state sensitivity to input and output optics during data acquisition is essentially non-existent. This enables relatively easy use of optic fibers, mirrors, lenses etc. for input/output.
A Search for relevant Patents was conducted. Most important is a Patent to Johs et al., U.S. Pat. No. 5,872,630, from which the present Application is derived as a CIP via intervening CIP Applications. Said 630 Patent describes:                A spectroscopic rotating compensator material system investigation system comprising a source of a polychromatic beam of electromagnetic radiation, a polarizer, a stage for supporting a material system, an analyzer, a dispersive optics and at least one detector system which contains a multiplicity of detector elements, said spectroscopic rotating compensator material system investigation system further comprising at least one compensator(s) positioned at a location selected from the group consisting of:                    before said stage for supporting a material system;            after said stage for supporting a material system; and            both before and after said stage for supporting a material system;                        such that when said spectroscopic rotating compensator material system investigation system is used to investigate a material system present on said stage for supporting a material system, said analyzer and polarizer are maintained essentially fixed in position and at least one of said at least one compensator(s) is caused to continuously rotate while a polychromatic beam of electromagnetic radiation produced by said source of a polychromatic beam of electromagnetic radiation is caused to pass through said polarizer and said compensator(s), said polychromatic beam of electromagnetic radiation being also caused to interact with said material system, pass through said analyzer and interact with said dispersive optics such that a multiplicity of essentially single wavelengths are caused to simultaneously enter a corresponding multiplicity of detector elements in said at least one detector system.        
Said 630 Patent also, amongst other disclosure, describes a mathematical regression based calibration procedure which makes possible the use of essentially any compensator regardless of non-achromatic characteristics.
Another Patent to Johs, from which the 630 Patent was continued-in part, is U.S. Pat No. 5,666,201, filed Sep. 20, 1995. The focus in said 201 Patent comprises a detector arrangement in which multiple orders of a dispersed beam of electromagnetic radiation are intercepted by multiple detector systems. However, claim 8 in the 201 Patent, in combination with a viewing the drawings therein, provide conception of the spectroscopic rotating compensator ellipsometer, as claimed in claim 1 of the Johs 630 Patent and, in fact, the 630 Patent issued in view of a terminal disclaimer based upon the 201 Patent. A CIP of the 630 Patent, is U.S. Pat. No. 6,353,477 to Johs et al. which describes preferred multiple element compensators.
Also disclosed is U.S. Pat. No. 5,706,212, Issued Jan. 6, 1998, and Filed Mar. 20, 1996 for an infrared ellipsometer system regression based calibration procedure. Said 212 Patent describes use of a substantially achromatic rotating compensator and application of mathematical regression in a calibration procedure which evaluates calibration parameters in both rotating and stationary components. The 212 Patent describes that 2 OMEGA and 4 OMEGA associated terms are generated by a detector of a signal which passes through a compensator caused to rotate at a rate of OMEGA. Said 630 Patent was continued-in-part therefrom, as is the present application via an intervening Patent application. It is noted that the 212 Patent application was filed four months prior to the earliest priority Patent Application, of Aspnes et al. Patents, (ie. U.S. Pat. Nos. 6,320,657, 6,134,012, 5,973,787 and 5,877,859), the later of which was Filed on Jul. 24, 1996. Additional Patents to Aspnes et al. include U.S. Pat. Nos. 7,173,700, 6,831,743, 6,650,415, 6,449,043 and 6,411,385. The Aspnes Patents describe broadband spectroscopic rotating compensator ellipsometer systems wherein the utility is found in the use of a “substantially non-achromatic” compensator, (see claim 1 in the 657 Patent), and selecting a wavelength range and compensator so that “an effective phase retardation value is induced covering at least from 90 degrees to 180 degrees”, (012 Patent), over a range of wavelengths of at least 200-800 nm. The 787 and 859 recite that at least one wavelength in said wavelength range has a retardation imposed of between 135 and 225 Degrees, and another wavelength in the wavelength range has a retardation imposed which is outside that retardation Range. The utility of the Therma-wave Patents derives from the identified conditions being met so that at least one of a 2 OMEGA and a 4 OMEGA coefficient provided by a detector provides usable information at a wavelength, even when said coefficient does not provide usable information at other wavelengths. Again, the identified Aspnes et al. Patents recite directly, or describe the presence of a “substantially-non-Achromatic” compensator, while, it is noted at this point, the invention disclosed in this Application utlizes what are properly termed substantially-achromatic or Psuedo-Achromatic compensators. It is further noted that the U.S. Pat. No. 5,716,212 Patent application, from which this Application continues-in-part, was filed prior to Jul. 24, 1976 filing date of the 859 Aspnes et al. priority Patent Application. The disclosed invention then has Priority to simultaneous use of 2 OMEGA and 4 OMEGA signals provided from a detector in a spectroscopic rotating compensator ellipsometer system which utilizes “other-than-substantially non-achromatic” compensators, namely “substantially-achromatic” or “pseudo-achromatic” compensators, to characterize samples, emphasis added.
A recently published PCT Application is No. WO 01/90687 A2, which is based on U.S. application Ser. No. 09/575,295 filed May 3, 2001. This Application was filed by Thermawave Inc. and specifically describes separate use of a 2ω and a 4ω term to provide insight to sample thickness and temperature.
Another Patent, U.S. Pat. No. 4,053,232 to Dill et al. describes a rotating-compensator ellipsometer system, which operates utilizes monochromatic light.
Two Patents which identify systems which utilize polychromatic light in investigation of material systems, U.S. Pat. Nos. 5,596,406 and 4,668,086 to Rosencwaig et al. and Redner, respectively, were also identified.
Also identified is a Patent to Woollam et al, U.S. Pat. No. 5,373,359 as it describes a rotating analyzer ellipsometer system which utilizes white light. Patents continued from the 359 Woollam et al. Patent are, U.S. Pat. Nos. 5,504,582 to Johs et al. and 5,521,706 to Green et al. Said 582 Johs et al. and 706 Green et al. Patents describe use of polychromatic light in a rotating analyzer ellipsometer system.
A Patent to Johs et al., U.S. Pat. No. 6,034,777 describes application of ellipsometry in an evacuated chamber comprising windows.
A Patent to Johs, U.S. Pat. No. 5,929,995 is disclosed as it describes application of ellipsometry in an evacuated chamber comprising windows.
A Patent to Bernoux et al., U.S. Pat. No. 5,329,357 is identified as it describes the use of optical fibers as input and output means in an ellipsometer system.
A Patent to Chen et al., U.S. Pat. No. 5,581,350 is identified as it describes the application of regression in calibration of ellipsometer systems.
Additionally, Patents pertaining to optical elements, and particularly to compensators/retarders per se are:
U.S. Pat. No. 4,917,461 to Goldstein, describes an achromatic infrared retarder comprised of two identical prisms in combination with a reflective surface;
U.S. Pat. No. 4,772,104 to Buhrer which describes an achromatic optical filter comprised of two birefringent disks;
U.S. Pat. No. 4,961,634 to Chipman describes an infrared achromatic retarder comprised of CdS and CdSe plates aligned with the fast axes thereof perpendicular to one another;
U.S. Pat. No. 6,181,421 to Aspnes et al., describes a tipped Berek plate compensator.
U.S. Pat. No. 5,946,098 to Johs, Herzinger and Green, describes numerous optical elements. In addition Patents to Johs et al. U.S. Pat. Nos. 6,084,674; 6,118,537; 6,100,981; 6,141,102; 6,100,981; 5,963,325; 6,084,674 and to Herzinger et al. U.S. Pat. No. 6,084,675, which Applications depend from application Ser. No. 08/997,311 filed Dec. 23, 1997, now said U.S. Pat. No. 5,946,098;
Additional Patents which describe compensators are U.S. Pat. No. 548,495 to Abbe; U.S. Pat. No. 4,556,292 to Mathyssek et al.; U.S. Pat. No. 5,475,525 Tournois et al.; U.S. Pat. No. 5,016,980 Waldron; and U.S. Pat. No. 3,817,624 to Martin and U.S. Pat. No. 2,447,828 to West;
And, Patents to Robert et al., U.S. Pat. Nos. 4,176,951 and 4,179,217 are also disclosed as they describe rotating birefringent elements in ellipsometers which produce 2ω and 4ω components.
A PCT Patent Application, No. WO 01/086257 is also known and is disclosed as it describes a combination of an aperture and lens to define a spot on a sample.
A Patent to Lacey et al., U.S. Pat. No. 5,793,480 is disclosed as it describes a field stop and lens combination in an ellipsometer prior to a sample.
A Patent to Spanier et al., U.S. Pat. No. 5,166,752 is disclosed as it describes an ellipsometer with lenses and apertures before and after a sample.
A Patents to Lessner et al., U.S. Pat. No. 4,054,812 describes a Source of Spectroscopic electromagnetic radiation which provides heat sink and ozone containment.
A Patent to Ellebracht et al., U.S. Pat. No. 4,322,165 is disclosed as it describes purging in a VUV plasma atomic emission spectroscopic instrument.
A Patent to Burns et al., U.S. Pat. No. 4,875,773 is disclosed as it describes an optical system for a multidetector array spectrograph.
A Patent to Freeouf, U.S. Pat. No. 6,414,302 is disclosed as it describes a high photon energy, (up through 10 eV), range reflected light characterization system.
A Patent to Aspnes et al., U.S. Pat. No. 5,091,320 is disclosed as it describes application of ellipsometry with an evacuated chamber.
A Patent to Hartley, U.S. Pat. No. 4,770,895 is disclosed as it describes application of ellipsometry with an evacuated chamber.
A Published Patent Application by McAninch, No, 2002/0149774 A1 is disclosed as it describes purging a measurement region near a substrate in a metrology tool.
A J. A. Woollam CO. Flyer titled VUV-VASE (Registered Trademark), is disclosed as it describes a monochromater based rotating analyzer ellipsomete system in a purged chamber.
A Patent to Ivarsson, U.S. Pat. No. 6,493,097 is disclosed as it describes a Detector Array in an analytical instrument using electromagnetic radiation.
A Patent to Stewart, U.S. Pat. No. 5,229,833 is disclosed as it describes an optical sensor comprising a CCD Array.
A Patent to Azzam, U.S. Pat. No. 5,337,146 is disclosed as it describes a spectrophotometer comprising a linear array detector.
A Patent to Wilkins et al., U.S. Pat. No. 6,031,619 describes an imaging spectrometer with a CCD matrix or row detector.
A Patent to Imai et al., U.S. Pat. No. 5,818,596 is disclosed as it describes use of purging gas to prevent contaminants on samples, but does hot disclose ellipsometry or a multiple detector element detector array.
A Published Patent Application by McAninch, No, 2002/0149774 A1 is disclosed as it describes purging a measurement region near a substrate in a metrology tool.
A Published Patent Application by Wang et al., No. 2003/0071996 A1 is disclosed as it involves purging of the environment of one beam in a system involving two beams.
A Published Patent Application by Eckert et al., No. US 2003/0150997 A1 is disclosed as it describes use of VUV wavelengths and purging.
Additional known relevant Patents are:
                U.S. Pat. No. 5,706,212 to Thompson et al.;        U.S. Pat. No. 6,353,477 to Johs et al.;        U.S. Pat. No. 5,963,325 to Johs et al.;        U.S. Pat. No. 6,141,102 to Johs et al.;        U.S. Pat. No. 6,084,675 to Herzinger et al. U.S. Pat. No. 6,118,537 to Johs et al.;        U.S. Pat. No. 6,100,981 to Johs et al.;        U.S. Pat. No. 6,084,674 to Johs et al.        U.S. Pat. No. 6,084,675 to Herzinger et al.Regarding Articles,        
An article by Johs, titled “Regression Calibration Method For Rotating Element Ellipsometers”, which appeared in Thin Film Solids, Vol. 234 in 1993 is also identified as it predates the Chen et al. Patent and describes an essentially similar approach to ellipsometer calibration.
An Article titled “A New Purged UV Spectroscopic Ellipsometer to Characterize Thin Films and Multilayers at 157 nm”, Boher et al., Proc. SPIE, Vol. 3998, (June 2000) is disclosed as it describes a UV spectroscopic ellipsometer in combination with purging.
A presentation titled “Characterisation of Thin Films and Multilayers in the VUV Wavelength Range Using Spectroscopic Ellipsometry and Spectroscopic Photometry”, Boher et al., 157 nm Symposium, May 2000) is disclosed as it describes a UV spectroscopic ellipsometer.
A paper titled “Progress in Spectroscopic Ellipsometry: Applications from Ultraviolet to Infrared”, Hilfiker et al., J. Vac. Sci. Technol. A, (July/August 2003).
A paper titled “Atomic Scale Characterization of Semiconductors by In-Situ Real Time Spectroscopic Ellipsometry”, Boher et al., Thin Solid Flims 318 (1998) is disclosed as it mentions multichannel detectors.
A paper titled “Optical Characterization in the Vacuum Ultraviolet with Variable Angle Spectroscopic Ellipsometry: 157 nm and below”, Hilfiker et al., Proc. SPIE Vol. 3998 (2000) is disclosed as it describes use of the J. A. Woollam CO. VUV-VASE which is a monochromater based purged system.
A paper titled “Feasibility and Applicability of Integrated Metrology Using Spectroscopic Ellipsometry in a Cluster Tool”, Boher et al., SPIE Vol. 4449, (2001) is disclosed as it describes a multichannel ellipsometer applied outside an environmental chamber. This application required electromagnetic radiation to pass through windows to reach a sample.
Four papers authored or co-authored by Collins, which describe use of multichannels and rotating element ellipsometers, including rotating compensator, but not in an environmental chamber are:                “Characterization of Wide Bandgap Thin Film Growth Using UV-Extended Real Time Spectroscopic Ellipsometry Applications to Cubic Boron Nitride”, Zapien et al., J. of Wide Bandgap Materials, Vol 9, No. 3 (January 2002);        “Automated Rotating Element Ellipsometers: Calibration, Operation, and Real-Time Applications”, Collins, Rev. Sci. Instrum. 61 (8) (aug. 1990);        “Waveform Analysis With Optical Multichannel Detectors: Applications for Rapid-Scan Spectroscopic Ellipsometers”, An et al., Rev. Sci. Instrum. 62(8), (August 1991); and        “Multichannel Ellipsometer for Real Time Spectroscopy of Thin Film Deposition for 1.5 to 6.5 eV”, Zapien et al., Rev. Sci. Instrum. Vol. 71, No. 9, (September 1991).        
A book by Azzam and Bashara titled “Ellipsometry and Polarized light” North-Holland, 1977 is disclosed and incorporated herein by reference for general theory.
As well, identified for authority regarding regression, is a book titled Numerical Recipes in “C”, 1988, Cambridge University Press.
Even in view of the prior art need remains for a rotating compensator ellipsometer that comprises a Detector system comprised of a multiplicity of detector elements, which detector elements simultaneously detect a multiplicity of wavelengths, said rotating compensator ellipsometer system being present in an environmental control chamber. Need further remains for compensator designs with substantially achromatic characteristics and which minimize deviation in the locus of a beam passed therethrough even while rotating.